Flexible tree structure

ABSTRACT

A method and apparatus for partitioning a block to permit the encoding or decoding of a video sequence includes partitioning the block using a split-to-square partition pattern, a horizontal binary tree partition pattern, or a horizontal ternary tree partition pattern to generate a set of sub-blocks, wherein a same priority is allocated to the split-to-square partition pattern, the horizontal binary tree partition pattern, and the horizontal ternary tree partition pattern such that the split-to-square partition pattern may be used before, after, or interleaved with the horizontal binary tree partition pattern and the horizontal ternary tree partition pattern. Encoding or decoding the video sequence is performed based on partitioning the block using the split-to-square partition pattern, the horizontal binary tree partition pattern, or the horizontal ternary tree partition pattern.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. § 119 to U.S.Application No. 62/639,989, filed on Mar. 7, 2018, in the United StatesPatent & Trademark Office, the disclosure of which is incorporatedherein by reference in its entirety.

FIELD

This disclosure is related to advanced block partitioning in hybridvideo coding beyond HEVC. More specifically, a flexible tree structureis proposed for efficient block partitioning.

BACKGROUND

ITU-T VCEG (Q6/16) and ISO/IEC MPEG (JTC 1/SC 29/WG 11) published theH.265/HEVC (High Efficiency Video Coding) standard in 2013 (version 1)2014 (version 2) 2015 (version 3) and 2016 (version 4). Since then theyhave been studying the potential need for standardization of futurevideo coding technology with a compression capability that significantlyexceeds that of the HEVC standard (including its extensions). The groupsare working together on this exploration activity in a jointcollaboration effort known as the Joint Video Exploration Team (JVET) toevaluate compression technology designs proposed by their experts inthis area. A Joint Exploration Model (JEM) has been developed by JVET toexplore the video coding technologies beyond the capability of HEVC, andthe current latest version of JEM is JEM-7.0.

In HEVC, a coding tree unit (CTU) is split into coding units (CUs) byusing a quadtree structure denoted as coding tree to adapt to variouslocal characteristics. The decision whether to code a picture area usinginter-picture (temporal) or intra-picture (spatial) prediction is madeat the CU level. Each CU can be further split into one, two, or fourprediction units (PUs) according to the PU splitting type. Inside onePU, the same prediction process is applied and the relevant informationis transmitted to the decoder on a PU basis. After obtaining theresidual block by applying the prediction process based on the PUsplitting type, a CU can be partitioned into transform units (TUs)according to another quadtree structure similar to the coding tree forthe CU. One of the key features of the HEVC structure is that it has themultiple partition conceptions including CU, PU, and TU. In HEVC, a CUor a TU can only be square shaped, while a PU may be square orrectangular shaped for an inter predicted block. In later stages ofHEVC, some contributions proposed to allow rectangular shaped PUs forintra prediction and transformation. These proposals were not adopted toHEVC but extended to be used in JEM. At the picture boundary, HEVCimposes implicit quad-tree split so that a block will keep quad-treesplitting until the size fits the picture boundary.

Inspired by previous works, a Quad-tree-Binary-tree (QTBT) structure wasdeveloped and unifies the concepts of the CU, PU, and TU and supportsmore flexibility for CU partitioned shapes. In the QTBT block structure,a CU can have either a square or rectangular shape. A coding tree unit(CTU) is first partitioned by a quadtree structure. The quadtree leafnodes are further partitioned by a binary tree structure. There are twosplitting types, symmetric horizontal splitting and symmetric verticalsplitting, in the binary tree splitting. The binary tree leaf nodes arecalled coding units (CUs), and that segmentation is used for predictionand transform processing without any further partitioning. This meansthat the CU, PU, and TU have the same block size in the QTBT codingblock structure. In JEM, a CU sometimes consists of coding blocks (CBs)of different colour components, e.g., one CU contains one luma CB andtwo chroma CBs in the case of P and B slices of the 4:2:0 chroma formatand sometimes consists of a CB of a single component, e.g., one CUcontains only one luma CB or just two chroma CBs in the case of Islices.

The following parameters are defined for the QTBT partitioning scheme:

-   -   CTU size: the root node size of a quadtree, the same concept as        in HEVC    -   MaxQTDepth: the maximum allowed quad-tree depth    -   MinQTSize: the minimum allowed quadtree leaf node size    -   MaxBTSize: the maximum allowed binary tree root node size    -   MaxBTDepth: the maximum allowed binary tree depth    -   MinBTSize: the minimum allowed binary tree leaf node size

In one example of the QTBT partitioning structure, the CTU size is setas 128×128 luma samples with two corresponding 64×64 blocks of chromasamples, the MinQTSize is set as 16×16, the MaxBTSize is set as 64×64,the MinBTSize (for both width and height) is set as 4×4, and theMaxBTDepth is set as 4. The quadtree partitioning is applied to the CTUfirst to generate quadtree leaf nodes. The quadtree leaf nodes may havea size from 16×16 (i.e., the MinQTSize) to 128×128 (i.e., the CTU size).If the leaf quadtree node is 128×128, it will not be further split bythe binary tree since the size exceeds the MaxBTSize (i.e., 64×64).Otherwise, the leaf quadtree node could be further partitioned by thebinary tree. Therefore, the quadtree leaf node is also the root node forthe binary tree and it has the binary tree depth as 0. When the binarytree depth reaches MaxBTDepth (i.e., 4), no further splitting isconsidered. When the binary tree node has width equal to MinBTSize(i.e., 4), no further horizontal splitting is considered. Similarly,when the binary tree node has height equal to MinBTSize, no furthervertical splitting is considered. The leaf nodes of the binary tree arefurther processed by prediction and transform processing without anyfurther partitioning. In the JEM, the maximum CTU size is 256×256 lumasamples.

In addition, the QTBT scheme supports the ability for the luma andchroma to have a separate QTBT structure. Currently, for P and B slices,the luma and chroma CTBs in one CTU share the same QTBT structure.However, for I slices, the luma CTB is partitioned into CUs by a QTBTstructure, and the chroma CTBs are partitioned into chroma CUs byanother QTBT structure. This means that a CU in an I slice consists of acoding block of the luma component or coding blocks of two chromacomponents, and a CU in a P or B slice consists of coding blocks of allthree colour components.

In HEVC, inter prediction for small blocks is restricted to reduce thememory access of motion compensation, such that bi-prediction is notsupported for 4×8 and 8×4 blocks, and inter prediction is not supportedfor 4×4 blocks. In the QTBT of the JEM, these restrictions are removed.

Multi-type-tree (MTT) structure is a more flexible tree structure thanQTBT. In MTT, tree types other than quad-tree and binary-tree aresupported. For example, horizontal and vertical center-side triple-treesare introduce. Further, MTT supports (a) quad-tree partitioning, (b)vertical binary-tree partitioning, (c) horizontal binary-treepartitioning, (d) vertical center-side triple-tree partitioning, (e)horizontal center-side triple-tree partitioning, among other types.

There are two levels of trees, region tree (quad-tree) and predictiontree (binary-tree or triple-tree). A CTU is firstly partitioned byregion tree (RT). A RT leaf may be further split with prediction tree(PT). A PT node may also be further split with PT until a max PT depthis reached. After entering PT, RT (quad-tree) cannot be used anymore. APT leaf is the basic coding unit. It is still called CU for convenience.A CU cannot be further split. Prediction and transform are both appliedon CU in the same way as JEM-3 or QTBT.

The key benefits of the triple-tree partitioning are to complementquad-tree and binary-tree partitioning: triple-tree partitioning is ableto capture objects which are located in a block center, while quad-treeand binary-tree are always splitting along the block center. Further,the width and height of the partitions of the proposed ternary trees arealways a power of two so that no additional transforms are needed.

The design of the two-level tree is mainly motivated by complexityreduction. Theoretically, the complexity of traversal of a tree isT^(D), where T denotes the number of split types, and D is the depth oftree. With the design of a two level tree and by restricting the firstlevel to quad-tree only (e.g., reduce the number of Tat certain levels),the complexity is significantly while maintaining reasonableperformance.

To further improve the coding efficiency on top of QTBT, an asymmetricbinary tree is proposed. For example, a coding unit with size S isdivided into 2 sub-CU with sizes S/4 and S/4, either in the horizontalor in the vertical direction. In practice the added available CU sizesare 12 and 24. In a further extended version of the tool, CU sizes 6 and48 may be allowed.

One major issue with this method is that it is inconvenient ifwidth/height of a block is not a power of two. For example, transformswith sizes such as 12 and 24 need to be supported. Special handling mayalso be needed when splitting a block with width/height other than apower of 2.

SUMMARY

According to an aspect of the disclosure, a method for partitioning ablock to permit the encoding or decoding of a video sequence includespartitioning the block using a split-to-square partition pattern, ahorizontal binary tree partition pattern, or a horizontal ternary treepartition pattern to generate a set of sub-blocks, wherein a samepriority is allocated to the split-to-square partition pattern, thehorizontal binary tree partition pattern, and the horizontal ternarytree partition pattern such that the split-to-square partition patternmay be used before, after, or interleaved with the horizontal binarytree partition pattern and the horizontal ternary tree partitionpattern; and encoding or decoding the video sequence based onpartitioning the block using the split-to-square partition pattern, thehorizontal binary tree partition pattern, or the horizontal ternary treepartition pattern.

According to an aspect of the disclosure, a method for partitioning ablock to permit the encoding or decoding of a video sequence includespartitioning the block using a split-to-square partition pattern togenerate a set of sub-blocks, wherein if the block is square, then eachsub-block is square, and wherein if the block is non-square, then eachsub-block includes a same size that is a greatest common factor of awidth and a height of the block; encoding or decoding the video sequencebased on partitioning the block using the split-to-square partitionpattern.

According to an aspect of the disclosure, a device for partitioning ablock to permit the encoding or decoding of a video sequence includes atleast one memory configured to store program code; at least oneprocessor configured to read the program code and operate as instructedby the program code, the program code including: partitioning codeconfigured to cause the at least one processor to partition the blockusing a split-to-square partition pattern, a horizontal binary treepartition pattern, or a horizontal ternary tree partition pattern togenerate a set of sub-blocks, wherein a same priority is allocated tothe split-to-square partition pattern, the horizontal binary treepartition pattern, and the horizontal ternary tree partition patternsuch that the split-to-square partition pattern may be used before,after, or interleaved with the horizontal binary tree partition patternand the horizontal ternary tree partition pattern; and encoding ordecoding code configured to cause the at least one processor to encodeor decode the video sequence based on partitioning the block using thesplit-to-square partition pattern, the horizontal binary tree partitionpattern, or the horizontal ternary tree partition pattern.

According to an aspect of the disclosure, a non-transitorycomputer-readable medium storing instructions, the instructionscomprising: one or more instructions that, when executed by one or moreprocessors of a device for partitioning a block to permit the encodingor decoding of a video sequence, cause the one or more processors to:partition the block using a split-to-square partition pattern, ahorizontal binary tree partition pattern, or a horizontal ternary treepartition pattern to generate a set of sub-blocks, wherein a samepriority is allocated to the split-to-square partition pattern, thehorizontal binary tree partition pattern, and the horizontal ternarytree partition pattern such that the split-to-square partition patternmay be used before, after, or interleaved with the horizontal binarytree partition pattern and the horizontal ternary tree partitionpattern; and encode or decode the video sequence based on partitioningthe block using the split-to-square partition pattern, the horizontalbinary tree partition pattern, or the horizontal ternary tree partitionpattern.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a flowchart of an example process for partitioning a blockusing a split-to-square partition pattern to generate a set ofsub-blocks.

FIG. 2 is a simplified block diagram of a communication system accordingto an embodiment of the present disclosure.

FIG. 3 is a diagram of the placement of a video encoder and decoder in astreaming environment.

FIG. 4 is a functional block diagram of a video decoder according to anembodiment of the present disclosure.

FIG. 5 is a functional block diagram of a video encoder according to anembodiment of the present disclosure.

FIG. 6 is a diagram of a computer system in accordance with anembodiment.

FIG. 7 is a flowchart of an example process for partitioning a blockusing a unified tree depth to generate a set of sub-blocks.

PROBLEM TO BE SOLVED

The two-level MTT tree structure is an unbalanced framework. As QT isnot allowed after BT/TT nodes, the overall depth may be much smaller fora tree starting from BT/TT than a tree starting from QT. Such anunbalanced tree design introduces problems for parallel encoding such asmulti-threading at depth 0 level at the encoder side sincemulti-threading will not help if one subtree occupies most of theencoding time.

The current design may degrade coding performance in some special cases.For example, in 4:2:2 chroma format, if a square luma CTU is used, anon-square chroma CTU occurs accordingly. In this way, significantcomputational expense is introduced.

HEVC implicit QT splitting is not efficient if flexible tree structureslike MTT are used since, sometimes, too small blocks must be selected byimplicit split.

DETAILED DESCRIPTION

FIG. 1 is a flowchart of an example process for partitioning a blockusing a split-to-square partition pattern to generate a set ofsub-blocks.

In some implementations, one or more process blocks of FIG. 1 may beperformed by a decoder. In some implementations, one or more processblocks of FIG. 1 may be performed by another device or a group ofdevices separate from or including a decoder, such as an encoder.

As shown in FIG. 1, a process may include determining whether a block issquare (block 110). If the block is square (block 110—YES), then theprocess may include partitioning the block using a split-to-squarepartition pattern to generate a set of sub-blocks (block 120). In thiscase, each sub-block is square. Alternatively, if the block isnon-square (block 110—NO), then the process may include partitioning theblock using a split-to-square partition pattern to generate a set ofnon-square sub-blocks (block 130). In this case, each sub-block includesa same size that is a greatest common factor of a width and height ofthe block. As further shown in FIG. 1, the process may include encodingor decoding the video sequence based on partitioning the block using thesplit-to-square partition pattern (block 140).

According to an embodiment, it is proposed to change the quad-tree splitto split-to-square. If the block to be split is square, thesplit-to-square has the same effect as the quad-tree split. Otherwise,the block is split into same-size square sub-blocks whose width/heightis the greatest common factor of the width and height of the block. Forexample, an 8×32 block is split into four 8×8 block withsplit-to-square.

According to an embodiment, the maximal number of sub-blocks may beconstrained by pre-definition or signaling. It may be signaled in thesequence parameter set (SPS), picture parameter set (PPS), slice header,CTU header, tile header, or for a region of a picture. According to anembodiment, the maximum number of sub-blocks may be 4, 8, 16, or thelike. When the maximum number of sub-blocks, pre-defined or signaled isconflict to the split-to-square signaling, for example, thesplit-to-square signaling indicates split-to-square for a 64×8 block,while the maximum number of sub-blocks is equal to 4, then in oneembodiment, the split-to-square flag is overwritten and the 64×8 blockis not further split-to-square. In another embodiment, when thissituation happens, the bitstream is considered as a non-conformingbitstream.

To avoid the duplication with other split types, such as binary tree,split-to-square or other split types are disallowed under certainconditions. When a partition or split is not allowed, the signaling ofthis partition or split may be eliminated. In this case, the relatedsignaling may be conditionally skipped.

Split-to-square is disallowed if there are two sub-blocks (both luma andchroma has two sub-blocks) after a split-to-square, and related binarytree is also allowed at the same time. For example, for a 16×8 blockboth split-to-square and vertical binary split lead to two 8×8sub-blocks. In this case, split-to-square is not allowed so that thesignal of split-to-square for the 16×8 block is skipped andsplit-to-square flag is derived as false.

Either split-to-square or vertical binary split is disallowed if the twolead to the same sub-block partitioning after split. Eithersplit-to-square or horizontal binary split is disallowed if the two leadto the same sub-block partitioning after split.

When luma and chroma share the same splitting tree, such as the case ininter slices in JEM, split-to-square may or may not be disallowed if aluma block and its associated chroma block have different shapes, suchas the case when video content is in 4:2:2 chroma format.

In one embodiment, split-to-square is disallowed if a luma block issquare or a luma block's associated chroma blocks are square. In anotherembodiment, split-to-square is allowed but may lead to different numberof sub-blocks for luma and chroma components. For example, for contentin 4:2:2 chroma format a 16×16 luma block associates two 8×16 blocks.With split-to-square, the luma block is split into four 8×8 sub-blockswhile each chroma block is split into two 8×8 sub-blocks. In anotherembodiment, split-to-square is allowed based on luma component. Chromablocks needs to have aligned partitioning to luma block. For example,for content in 4:2:2 chroma format, a 16×16 luma block associates two8×16 blocks. With split-to-square, the luma block is split into four 8×8sub-blocks while each chroma block is split into four 4×8 sub-blocks.

In another embodiment, split-to-square is allowed based on chromacomponent. Luma blocks needs to have aligned partitioning to chromablocks. For example, for content in 4:2:2 chroma format, a 16×16 lumablock associates two (Cb and Cr) 8×16 blocks. With split-to-square, eachchroma is split into two 8×8 sub-blocks while the luma block is splitinto four 8×8 sub-blocks.

According to an embodiment, at the picture boundary, certain tree typesmay be conditionally disallowed. For example, if a block to be split isvertically outside the picture boundary but not horizontally, verticalsplits, such as vertical binary tree and vertical ternary tree, aredisallowed for this block. As another example, if a block to be split ishorizontally outside the picture boundary but not vertically, horizontalsplits, such as horizontal binary tree and horizontal ternary tree, asdisallowed for this block.

According to an embodiment, it is proposed to allow different values ofwidth and height for the largest luma block and/or largest chroma blockwhile keeping the smallest luma block as square. The width and height ofCTU are signaled in bitstream, such as in SPS, PPS, or slice header. Thewidth of the minimal luma block is signaled in bitstream, such as inSPS, PPS, or slice header. The height of the minimal luma block isinferred the same as the width.

According to an embodiment, it is proposed to give the same priority tosplit-to-square, BT and TT so that 1) unified tree depth replaces QTdepth and BT depth; 2) split-to-square may be at any position, beforeBT/TT, after BT/TT, or interleaved with BT/TT. At encoder side, all treetypes including but not limited to split-to-square, vertical binarytree, horizontal binary tree, vertical ternary tree, and horizontalternary tree have the same maximal depth and similar searchingcomplexity in general. Consequently, encoder may use multi-threading(one thread for one tree type) to find the best splitting tree inparallel.

As an example, for a 128×128 block, at depth 0, a binary split is used.At depth 1, a binary split and a triple split are employed for top andbottom sub-blocks, respectively. At depth 2, a split-to-square is usedto split the 128×32 sub-block into four 32×32 sub-blocks. Finally, atdepth 3, a 32×32 block is further split into four 16×16 sub-blocks withsplit-to-square.

According to an embodiment, it is proposed to always signal the treetype (split type) including picture boundary with a certain tree typebinarization table such that certain bins may be derived instead ofsignaled at picture boundary. As an example, the binarization table maybe shown as follows:

Tree Types Bin0 Bin1 Bin2 Bin3 Non-split 0 Split-to-square 1 1Horizontal binary tree 1 0 0 0 Horizontal ternary tree 1 0 0 1 Verticalbinary tree 1 0 1 0 Vertical ternary tree 1 0 1 1

The four bins in the table above represent the split type, such aswhether to split, whether to split to square, vertical or horizontal,and triple or binary tree, respectively. For a block at the pictureboundary and a part of the block is outside the picture, the binindicating whether split (Bin0 in this embodiment) is not signaled butderived as 1, namely split. Alternatively, the bin indicating verticalor horizontal (Bin2 in this embodiment) is not signaled but derivedif 1) the bin indicating split-to-square is 0 (Bin1 in this embodiment),and 2) the block is only vertically or only horizontally outside thepicture but not both.

According to an embodiment, it is proposed that the binarization tablemay depend on other coded information or any other information that isknown to both encoder and decoder, including, but not limited to: blockarea size, block height and/or width, block shape, quantizationparameter (QP), luma or chroma component, intra or inter coded, temporallayer, CTU size, block splitting depth. In one example embodiment,several binarization tables may be pre-defined for both encoder anddecoder, and the selection may be signaled in slice header, SPS, PPS,VPS or per CTU. In another example embodiment, two binarization tablesfor the splitting type are pre-defined, if the current block area sizeis greater than a pre-defined threshold, e.g., 1024, one of the twotables is used for binarizing the split type, otherwise, the other tableis used for binarizing the split type.

According to an embodiment, it is proposed to check the parent blocksplit (or partition tree) types and the neighboring split (or partitiontree) type when deciding split type and/or direction for the currentblock. Partitioning duplications due to different splitting orders aredisallowed. In one example embodiment, the two splitting orders shown inthe figure below lead to the same partitioning. For example, a block isfirst split with vertical binary tree and then the two sub-blocks aresplit with horizontal binary tree. Further, a block is first split withhorizontal binary tree and then the two sub-blocks are split withvertical binary tree. To avoid duplication, either the 3^(rd) splits isdisallowed.

In another example, if the parent (last depth) coding or predictionblock of the current coding or prediction block is split verticallyusing ternary tree to three sub-blocks, then the second (or middle)sub-block shall not allow further vertically binary split.

In another example, if the parent (last depth) coding or predictionblock of the current coding or prediction block is split horizontallyusing ternary tree to three sub-blocks, then the second (or middle)sub-block shall not allow further horizontally binary split.

According to an embodiment, it is proposed to indicate the availabilityof all possibilities of partition traces (a partition trace is how ablock is partitioned to a given partition pattern, i.e., the partitiontype of each depth) in a pre-defined look-up table that is accessible toboth encoder and decoder. When deciding whether a split type and/ordirection is allowed or signaled, the corresponding partition will beconverted to a number and indexed to the pre-defined look-up table, andthe availability is given from that look-up table, if the correspondingpartition is not available, then the splitting will not be signaled orallowed.

In one example embodiment, the availability of all partitionpossibilities is stored in terms of CTU, e.g., 64×64, 128×128 or256×256. In one example embodiment, two partition traces are indexed bym and n, m and n are integer numbers. In a first partition trace, theblock is first split as 4 square sub-blocks by quad tree, then eachsub-block is further split to 4 square sub-blocks by quad tree. In thesecond partition trace, the block is first split horizontally as 2rectangular sub-blocks by binary tree, then each sub-block is furthersplit horizontally as 2 rectangular sub-blocks by binary tree, finally,each sub-block is further split by split-to-square as 4 square blocks.It can be seen that these two partition traces result in the same finalpartition pattern, therefore, in this example, the right partition traceis marked as unavailable in the look-up table indexed by n, such thatthe signaling of the bottom rectangular block indicating furtherpartitioning to 4 square blocks is saved.

According to an embodiment, it is proposed to add vertically quad-treesplit (VQT) and horizontally quad-tree split (HQT). For example, a 32×32block can be split into four 8×32 blocks with vertically quad-tree splitor split into four 32×8 blocks with horizontally quad-tree split. Inanother embodiment, vertical QT and horizontal QT are only allowed forintra coded slice.

According to another embodiment, it is proposed to signal a flexibletree flag in the SPS, PPS or slice header to indicate whether the quadsplit is allowed after a binary split or not. If the flexible tree flagis equal to 1, the quad split is allowed after binary split. If theflexible tree flag is equal to 0, the quad split is not allowed afterbinary split. A syntax table example of the flexible tree flag in SPS isprovided as below. PPS and slice header signaling can follow the similarway.

Although FIG. 1 shows example blocks of an example process, in someimplementations, the process may include additional blocks, fewerblocks, different blocks, or differently arranged blocks than thosedepicted in FIG. 1. Additionally, or alternatively, two or more of theblocks of the process may be performed in parallel.

FIG. 2 illustrates a simplified block diagram of a communication system(200) according to an embodiment of the present disclosure. Thecommunication system (200) may include at least two terminals (210-220)interconnected via a network (250). For unidirectional transmission ofdata, a first terminal (210) may code video data at a local location fortransmission to the other terminal (220) via the network (250). Thesecond terminal (220) may receive the coded video data of the otherterminal from the network (250), decode the coded data and display therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

FIG. 2 illustrates a second pair of terminals (230, 240) provided tosupport bidirectional transmission of coded video that may occur, forexample, during videoconferencing. For bidirectional transmission ofdata, each terminal (230, 240) may code video data captured at a locallocation for transmission to the other terminal via the network (250).Each terminal (230, 240) also may receive the coded video datatransmitted by the other terminal, may decode the coded data and maydisplay the recovered video data at a local display device.

In FIG. 2, the terminals (210-240) may be illustrated as servers,personal computers and smart phones but the principles of the presentdisclosure are not so limited. Embodiments of the present disclosurefind application with laptop computers, tablet computers, media playersand/or dedicated video conferencing equipment. The network (250)represents any number of networks that convey coded video data among theterminals (210-240), including for example wireline and/or wirelesscommunication networks. The communication network (250) may exchangedata in circuit-switched and/or packet-switched channels. Representativenetworks include telecommunications networks, local area networks, widearea networks and/or the Internet. For the purposes of the presentdiscussion, the architecture and topology of the network (250) may beimmaterial to the operation of the present disclosure unless explainedherein below.

FIG. 3 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and decoder in astreaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (313), that caninclude a video source (301), for example a digital camera, creating,for example, an uncompressed video sample stream (302). That samplestream (302), depicted as a bold line to emphasize a high data volumewhen compared to encoded video bitstreams, can be processed by anencoder (303) coupled to the camera 301). The encoder (303) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video bitstream (304), depicted as a thin line toemphasize the lower data volume when compared to the sample stream, canbe stored on a streaming server (305) for future use. One or morestreaming clients (306, 308) can access the streaming server (305) toretrieve copies (307, 309) of the encoded video bitstream (304). Aclient (306) can include a video decoder (310) which decodes theincoming copy of the encoded video bitstream (307) and creates anoutgoing video sample stream (311) that can be rendered on a display(312) or other rendering device (not depicted). In some streamingsystems, the video bitstreams (304, 307, 309) can be encoded accordingto certain video coding/compression standards. Examples of thosestandards include ITU-T Recommendation H.265. Under development is avideo coding standard informally known as Versatile Video Coding (VVC).The disclosed subject matter may be used in the context of VVC.

FIG. 4 may be a functional block diagram of a video decoder (310)according to an embodiment of the present invention.

A receiver (410) may receive one or more codec video sequences to bedecoded by the decoder (310); in the same or another embodiment, onecoded video sequence at a time, where the decoding of each coded videosequence is independent from other coded video sequences. The codedvideo sequence may be received from a channel (412), which may be ahardware/software link to a storage device which stores the encodedvideo data. The receiver (410) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (410) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (415) may be coupled inbetween receiver (410) and entropy decoder/parser (420) (“parser”henceforth). When receiver (410) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosychronous network, the buffer (415) may not be needed, or can besmall. For use on best effort packet networks such as the Internet, thebuffer (415) may be required, can be comparatively large and canadvantageously of adaptive size.

The video decoder (310) may include a parser (420) to reconstructsymbols (421) from the entropy coded video sequence. Categories of thosesymbols include information used to manage operation of the decoder(310), and potentially information to control a rendering device such asa display (312) that is not an integral part of the decoder but can becoupled to it, as was shown in FIG. 4. The control information for therendering device(s) may be in the form of Supplementary EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (420) mayparse/entropy-decode the coded video sequence received. The coding ofthe coded video sequence can be in accordance with a video codingtechnology or standard, and can follow principles well known to a personskilled in the art, including variable length coding, Huffman coding,arithmetic coding with or without context sensitivity, and so forth. Theparser (420) may extract from the coded video sequence, a set ofsubgroup parameters for at least one of the subgroups of pixels in thevideo decoder, based upon at least one parameters corresponding to thegroup. Subgroups can include Groups of Pictures (GOPs), pictures, tiles,slices, macroblocks, Coding Units (CUs), blocks, Transform Units (TUs),Prediction Units (PUs) and so forth. The entropy decoder/parser may alsoextract from the coded video sequence information such as transformcoefficients, quantizer parameter (QP) values, motion vectors, and soforth.

The parser (420) may perform entropy decoding/parsing operation on thevideo sequence received from the buffer (415), so to create symbols(421). The parser (420) may receive encoded data, and selectively decodeparticular symbols (421). Further, the parser (420) may determinewhether the particular symbols (421) are to be provided to a MotionCompensation Prediction unit (453), a scaler/inverse transform unit(451), an Intra Prediction Unit (452), or a loop filter (456).

Reconstruction of the symbols (421) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (420). The flow of such subgroup control information between theparser (420) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, decoder (310) can beconceptually subdivided into a number of functional units as describedbelow. In a practical implementation operating under commercialconstraints, many of these units interact closely with each other andcan, at least partly, be integrated into each other. However, for thepurpose of describing the disclosed subject matter, the conceptualsubdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (451). Thescaler/inverse transform unit (451) receives quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (621) from the parser (420). It can output blockscomprising sample values, that can be input into aggregator (455).

In some cases, the output samples of the scaler/inverse transform (451)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (452). In some cases, the intra pictureprediction unit (452) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current (partly reconstructed) picture(454). The aggregator (455), in some cases, adds, on a per sample basis,the prediction information the intra prediction unit (452) has generatedto the output sample information as provided by the scaler/inversetransform unit (451).

In other cases, the output samples of the scaler/inverse transform unit(451) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a Motion Compensation Prediction unit (453) canaccess reference picture memory (457) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (421) pertaining to the block, these samples can beadded by the aggregator (455) to the output of the scaler/inversetransform unit (in this case called the residual samples or residualsignal) so to generate output sample information. The addresses withinthe reference picture memory form where the motion compensation unitfetches prediction samples can be controlled by motion vectors,available to the motion compensation unit in the form of symbols (421)that can have, for example X, Y, and reference picture components.Motion compensation also can include interpolation of sample values asfetched from the reference picture memory when sub-sample exact motionvectors are in use, motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (455) can be subject to variousloop filtering techniques in the loop filter unit (456). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video bitstream andmade available to the loop filter unit (456) as symbols (421) from theparser (420), but can also be responsive to meta-information obtainedduring the decoding of previous (in decoding order) parts of the codedpicture or coded video sequence, as well as responsive to previouslyreconstructed and loop-filtered sample values.

The output of the loop filter unit (456) can be a sample stream that canbe output to the render device (312) as well as stored in the referencepicture memory (456) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. Once a coded picture is fullyreconstructed and the coded picture has been identified as a referencepicture (by, for example, parser (420)), the current reference picture(656) can become part of the reference picture buffer (457), and a freshcurrent picture memory can be reallocated before commencing thereconstruction of the following coded picture.

The video decoder (310) may perform decoding operations according to apredetermined video compression technology that may be documented in astandard, such as ITU-T Rec. H.265. The coded video sequence may conformto a syntax specified by the video compression technology or standardbeing used, in the sense that it adheres to the syntax of the videocompression technology or standard, as specified in the videocompression technology document or standard and specifically in theprofiles document therein. Also necessary for compliance can be that thecomplexity of the coded video sequence is within bounds as defined bythe level of the video compression technology or standard. In somecases, levels restrict the maximum picture size, maximum frame rate,maximum reconstruction sample rate (measured in, for example megasamplesper second), maximum reference picture size, and so on. Limits set bylevels can, in some cases, be further restricted through HypotheticalReference Decoder (HRD) specifications and metadata for HRD buffermanagement signaled in the coded video sequence.

In an embodiment, the receiver (410) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (310) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal-to-noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 5 may be a functional block diagram of a video encoder (303)according to an embodiment of the present disclosure.

The encoder (303) may receive video samples from a video source (301)(that is not part of the encoder) that may capture video image(s) to becoded by the encoder (303).

The video source (301) may provide the source video sequence to be codedby the encoder (303) in the form of a digital video sample stream thatcan be of any suitable bit depth (for example: 8 bit, 10 bit, 12 bit, .. . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ) and anysuitable sampling structure (for example Y CrCb 4:2:0, Y CrCb 4:4:4). Ina media serving system, the video source (301) may be a storage devicestoring previously prepared video. In a videoconferencing system, thevideo source (303) may be a camera that captures local image informationas a video sequence. Video data may be provided as a plurality ofindividual pictures that impart motion when viewed in sequence. Thepictures themselves may be organized as a spatial array of pixels,wherein each pixel can comprise one or more samples depending on thesampling structure, color space, etc. in use. A person skilled in theart can readily understand the relationship between pixels and samples.The description below focuses on samples.

According to an embodiment, the encoder (303) may code and compress thepictures of the source video sequence into a coded video sequence (543)in real time or under any other time constraints as required by theapplication. Enforcing appropriate coding speed is one function ofController (550). Controller controls other functional units asdescribed below and is functionally coupled to these units. The couplingis not depicted for clarity. Parameters set by controller can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. A person skilled in the art can readily identify other functionsof controller (550) as they may pertain to video encoder (303) optimizedfor a certain system design.

Some video encoders operate in what a person skilled in the art readilyrecognizes as a “coding loop.” As an oversimplified description, acoding loop can consist of the encoding part of an encoder (530)(“source coder” henceforth) (responsible for creating symbols based onan input picture to be coded, and a reference picture(s)), and a (local)decoder (533) embedded in the encoder (303) that reconstructs thesymbols to create the sample data that a (remote) decoder also wouldcreate (as any compression between symbols and coded video bitstream islossless in the video compression technologies considered in thedisclosed subject matter). That reconstructed sample stream is input tothe reference picture memory (534). As the decoding of a symbol streamleads to bit-exact results independent of decoder location (local orremote), the reference picture buffer content is also bit exact betweenlocal encoder and remote encoder. In other words, the prediction part ofan encoder “sees” as reference picture samples exactly the same samplevalues as a decoder would “see” when using prediction during decoding.This fundamental principle of reference picture synchronicity (andresulting drift, if synchronicity cannot be maintained, for examplebecause of channel errors) is well known to a person skilled in the art.

The operation of the “local” decoder (533) can be the same as of a“remote” decoder (310), which has already been described in detail abovein conjunction with FIG. 4. Briefly referring also to FIG. 5, however,as symbols are available and en/decoding of symbols to a coded videosequence by entropy coder (545) and parser (420) can be lossless, theentropy decoding parts of decoder (310), including channel (412),receiver (410), buffer (415), and parser (420) may not be fullyimplemented in local decoder (533).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. The description of encodertechnologies can be abbreviated as they are the inverse of thecomprehensively described decoder technologies. Only in certain areas amore detail description is required and provided below.

As part of its operation, the source coder (530) may perform motioncompensated predictive coding, which codes an input frame predictivelywith reference to one or more previously-coded frames from the videosequence that were designated as “reference frames.” In this manner, thecoding engine (532) codes differences between pixel blocks of an inputframe and pixel blocks of reference frame(s) that may be selected asprediction reference(s) to the input frame.

The local video decoder (533) may decode coded video data of frames thatmay be designated as reference frames, based on symbols created by thesource coder (530). Operations of the coding engine (532) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 5), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (533) replicates decodingprocesses that may be performed by the video decoder on reference framesand may cause reconstructed reference frames to be stored in thereference picture cache (534). In this manner, the encoder (303) maystore copies of reconstructed reference frames locally that have commoncontent as the reconstructed reference frames that will be obtained by afar-end video decoder (absent transmission errors).

The predictor (535) may perform prediction searches for the codingengine (532). That is, for a new frame to be coded, the predictor (535)may search the reference picture memory (534) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(535) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (535), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (534).

The controller (550) may manage coding operations of the video coder(530), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (545). The entropy coder translatesthe symbols as generated by the various functional units into a codedvideo sequence, by loss-less compressing the symbols according totechnologies known to a person skilled in the art as, for exampleHuffman coding, variable length coding, arithmetic coding, and so forth.

The transmitter (540) may buffer the coded video sequence(s) as createdby the entropy coder (545) to prepare it for transmission via acommunication channel (560), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(540) may merge coded video data from the video coder (530) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (550) may manage operation of the encoder (303). Duringcoding, the controller (550) may assign to each coded picture a certaincoded picture type, which may affect the coding techniques that may beapplied to the respective picture. For example, pictures often may beassigned as one of the following frame types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other frame in the sequence as a source of prediction.Some video codecs allow for different types of Intra pictures,including, for example Independent Decoder Refresh Pictures. A personskilled in the art is aware of those variants of I pictures and theirrespective applications and features.

A Predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A Bi-directionally Predictive Picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded non-predictively,via spatial prediction or via temporal prediction with reference to onepreviously coded reference pictures. Blocks of B pictures may be codednon-predictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video coder (303) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video coder (303) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (540) may transmit additional datawith the encoded video. The video coder (530) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, Supplementary EnhancementInformation (SEI) messages, Visual Usability Information (VUI) parameterset fragments, and so on.

Further, the proposed methods may be implemented by processing circuitry(e.g., one or more processors or one or more integrated circuits). Inone example, the one or more processors execute a program that is storedin a non-transitory computer-readable medium to perform one or more ofthe proposed methods.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 6 shows a computersystem 1200 suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by computer central processing units (CPUs),Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 6 for computer system 1200 are exemplary innature and are not intended to suggest any limitation as to the scope ofuse or functionality of the computer software implementing embodimentsof the present disclosure. Neither should the configuration ofcomponents be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system 1200.

Computer system 1200 may include certain human interface input devices.Such a human interface input device may be responsive to input by one ormore human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard 601, mouse 602, trackpad 603, touch screen 610,data-glove 1204, joystick 605, microphone 606, scanner 607, camera 608.

Computer system 1200 may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen 610, data-glove 1204, or joystick 605, but there can alsobe tactile feedback devices that do not serve as input devices), audiooutput devices (such as: speakers 609, headphones (not depicted)),visual output devices (such as screens 610 to include cathode ray tube(CRT) screens, liquid-crystal display (LCD) screens, plasma screens,organic light-emitting diode (OLED) screens, each with or withouttouch-screen input capability, each with or without tactile feedbackcapability—some of which may be capable to output two dimensional visualoutput or more than three dimensional output through means such asstereographic output; virtual-reality glasses (not depicted),holographic displays and smoke tanks (not depicted)), and printers (notdepicted).

Computer system 1200 can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW620 with CD/DVD or the like media 621, thumb-drive 622, removable harddrive or solid state drive 623, legacy magnetic media such as tape andfloppy disc (not depicted), specialized ROM/ASIC/PLD based devices suchas security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system 1200 can also include interface(s) to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include global systems for mobile communications(GSM), third generation (3G), fourth generation (4G), fifth generation(5G), Long-Term Evolution (LTE), and the like, TV wireline or wirelesswide area digital networks to include cable TV, satellite TV, andterrestrial broadcast TV, vehicular and industrial to include CANBus,and so forth. Certain networks commonly require external networkinterface adapters that attached to certain general purpose data portsor peripheral buses (649) (such as, for example universal serial bus(USB) ports of the computer system 1200; others are commonly integratedinto the core of the computer system 1200 by attachment to a system busas described below (for example Ethernet interface into a PC computersystem or cellular network interface into a smartphone computer system).Using any of these networks, computer system 1200 can communicate withother entities. Such communication can be uni-directional, receive only(for example, broadcast TV), uni-directional send-only (for exampleCANbus to certain CANbus devices), or bi-directional, for example toother computer systems using local or wide area digital networks.Certain protocols and protocol stacks can be used on each of thosenetworks and network interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core 640 of thecomputer system 1200.

The core 640 can include one or more Central Processing Units (CPU) 641,Graphics Processing Units (GPU) 642, specialized programmable processingunits in the form of Field Programmable Gate Areas (FPGA) 643, hardwareaccelerators for certain tasks 644, and so forth. These devices, alongwith Read-only memory (ROM) 645, Random-access memory (RAM) 646,internal mass storage such as internal non-user accessible hard drives,solid-state drives (SSDs), and the like 647, may be connected through asystem bus 1248. In some computer systems, the system bus 1248 can beaccessible in the form of one or more physical plugs to enableextensions by additional CPUs, GPU, and the like. The peripheral devicescan be attached either directly to the core's system bus 1248, orthrough a peripheral bus 649. Architectures for a peripheral bus includeperipheral component interconnect (PCI), USB, and the like.

CPUs 641, GPUs 642, FPGAs 643, and accelerators 644 can execute certaininstructions that, in combination, can make up the aforementionedcomputer code. That computer code can be stored in ROM 645 or RAM 646.Transitional data can be also be stored in RAM 646, whereas permanentdata can be stored for example, in the internal mass storage 647. Faststorage and retrieve to any of the memory devices can be enabled throughthe use of cache memory, that can be closely associated with one or moreCPU 641, GPU 642, mass storage 647, ROM 645, RAM 646, and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture 1200, and specifically the core 640 can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core 640 that are of non-transitorynature, such as core-internal mass storage 647 or ROM 645. The softwareimplementing various embodiments of the present disclosure can be storedin such devices and executed by core 640. A computer-readable medium caninclude one or more memory devices or chips, according to particularneeds. The software can cause the core 640 and specifically theprocessors therein (including CPU, GPU, FPGA, and the like) to executeparticular processes or particular parts of particular processesdescribed herein, including defining data structures stored in RAM 646and modifying such data structures according to the processes defined bythe software. In addition or as an alternative, the computer system canprovide functionality as a result of logic hardwired or otherwiseembodied in a circuit (for example: accelerator 644), which can operatein place of or together with software to execute particular processes orparticular parts of particular processes described herein. Reference tosoftware can encompass logic, and vice versa, where appropriate.Reference to a computer-readable media can encompass a circuit (such asan integrated circuit (IC)) storing software for execution, a circuitembodying logic for execution, or both, where appropriate. The presentdisclosure encompasses any suitable combination of hardware andsoftware.

FIG. 7 is a flowchart of an example process for partitioning a blockusing a unified tree depth to generate a set of sub-blocks.

As shown in FIG. 7, the example process may include partitioning theblock using a split-to-square partition pattern, a horizontal binarytree partition pattern, or a horizontal ternary tree partition patternto generate a set of sub-blocks (block 710). A same priority isallocated to the split-to-square partition pattern, the horizontalbinary tree partition pattern, and the horizontal ternary tree partitionpattern such that the split-to-square partition pattern may be usedbefore, after, or interleaved with the horizontal binary tree partitionpattern and the horizontal ternary tree partition pattern.

As further shown in FIG. 7, the process may include determining whetheranother partition is to be performed (block 720).

If another partition is to be performed (block 720—YES), then theprocess may return to block 710. Otherwise, as further shown in FIG. 7,the example process may include encoding or decoding the video sequencebased on partitioning the block using the split-to-square partitionpattern, the horizontal binary tree partition pattern, or the horizontalternary tree partition pattern (block 730).

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

1. A method for partitioning a block to permit the encoding or decodingof a video sequence, the method comprising: partitioning the block usinga split-to-square partition pattern, a horizontal binary tree partitionpattern, or a horizontal ternary tree partition pattern to generate aset of sub-blocks, wherein a same priority is allocated to thesplit-to-square partition pattern, the horizontal binary tree partitionpattern, and the horizontal ternary tree partition pattern such that thesplit-to-square partition pattern may be used before, after, orinterleaved with the horizontal binary tree partition pattern and thehorizontal ternary tree partition pattern; and encoding or decoding thevideo sequence based on partitioning the block using the split-to-squarepartition pattern, the horizontal binary tree partition pattern, or thehorizontal ternary tree partition pattern.
 2. The method of claim 1,wherein the block is partitioned using a split-to-square partitionpattern to generate the set of sub-blocks, wherein if the block issquare, then each sub-block is square, and wherein if the block isnon-square, then each sub-block includes a same size that is a greatestcommon factor of a width and a height of the block.
 3. The method ofclaim 1, further comprising: determining that the block is locatedvertically outside of a picture boundary, and is located horizontallyinside of the picture boundary; and preventing a partition using avertical split partition pattern.
 4. The method of claim 1, furthercomprising: determining that the block is located horizontally outsideof the picture boundary, and is located vertically inside of the pictureboundary; and preventing a partition using a horizontal split partitionpattern.
 5. The method of claim 1, further comprising: partitioning atleast one sub-block of the set of sub-blocks using the horizontal binarytree partition pattern after partitioning the block using thesplit-to-square partition pattern.
 6. The method of claim 1, furthercomprising: partitioning at least one sub-block of the set of sub-blocksusing the horizontal ternary tree partition pattern after partitioningthe block using the split-to-square partition pattern.
 7. The method ofclaim 1, further comprising: partitioning at least one sub-block using avertically quad-tree split (VQT) partition pattern.
 8. The method ofclaim 1, further comprising: partitioning at least one sub-block using ahorizontally quad-tree split (HQT) partition pattern.
 9. The method ofclaim 1, wherein the split-to-square partition pattern is used beforethe horizontal binary tree partition pattern and the horizontal ternarytree partition pattern
 10. The method of claim 1, wherein thesplit-to-square partition pattern is used after the horizontal binarytree partition pattern and the horizontal ternary tree partitionpattern.
 11. A device for partitioning a block to permit the encoding ordecoding of a video sequence, comprising: at least one memory configuredto store program code; and at least one processor configured to read theprogram code and operate as instructed by the program code, the programcode including: partitioning code configured to cause the at least oneprocessor to partition the block using a split-to-square partitionpattern, a horizontal binary tree partition pattern, or a horizontalternary tree partition pattern to generate a set of sub-blocks, whereina same priority is allocated to the split-to-square partition pattern,the horizontal binary tree partition pattern, and the horizontal ternarytree partition pattern such that the split-to-square partition patternmay be used before, after, or interleaved with the horizontal binarytree partition pattern and the horizontal ternary tree partitionpattern; and encoding or decoding code configured to cause the at leastone processor to encode or decode the video sequence based onpartitioning the block using the split-to-square partition pattern, thehorizontal binary tree partition pattern, or the horizontal ternary treepartition pattern.
 12. The device of claim 11, wherein a maximum numberof sub-blocks is four, eight, or sixteen.
 13. The device of claim 11,further comprising: determining code configured to cause the at leastone processor to determine that the block is located vertically outsideof a picture boundary, and is located horizontally inside of the pictureboundary; and preventing code configured to cause the at least oneprocessor to prevent a partition using a vertical split partitionpattern.
 14. The device of claim 11, further comprising: determiningcode configured to cause the at least one processor to determine thatthe block is located horizontally outside of the picture boundary, andis located vertically inside of the picture boundary; and preventingcode configured to cause the at least one processor to prevent apartition using a horizontal split partition pattern.
 15. The device ofclaim 11, wherein the partitioning code is further configured to causethe at least one processor to partition at least one sub-block of theset of sub-blocks using the horizontal binary tree partition patternafter partitioning the block using the split-to-square partitionpattern.
 16. The device of claim 11, wherein the partitioning code isfurther configured to cause the at least one processor to partition atleast one sub-block of the set of sub-blocks using the horizontalternary tree partition pattern after partitioning the block using thesplit-to-square partition pattern.
 17. The device of claim 11, whereinthe partitioning code is further configured to cause the at least oneprocessor to partition at least one sub-block using a verticallyquad-tree split (VQT) partition pattern.
 18. The device of claim 11,wherein the partitioning code is further configured to cause the atleast one processor to partition at least one sub-block using ahorizontally quad-tree split (HQT) partition pattern.
 19. The device ofclaim 11, wherein the block is partitioned using a split-to-squarepartition pattern to generate the set of sub-blocks, wherein if theblock is square, then each sub-block is square, and wherein if the blockis non-square, then each sub-block includes a same size that is agreatest common factor of a width and a height of the block.
 20. Anon-transitory computer-readable medium storing instructions, theinstructions comprising: one or more instructions that, when executed byone or more processors of a device for partitioning a block to permitthe encoding or decoding of a video sequence, cause the one or moreprocessors to: partition the block using a split-to-square partitionpattern, a horizontal binary tree partition pattern, or a horizontalternary tree partition pattern to generate a set of sub-blocks, whereina same priority is allocated to the split-to-square partition pattern,the horizontal binary tree partition pattern, and the horizontal ternarytree partition pattern such that the split-to-square partition patternmay be used before, after, or interleaved with the horizontal binarytree partition pattern and the horizontal ternary tree partitionpattern; and encode or decode the video sequence based on partitioningthe block using the split-to-square partition pattern, the horizontalbinary tree partition pattern, or the horizontal ternary tree partitionpattern.